Substantially transparent linear light source

ABSTRACT

An apparatus and method for coupling light into a light source in the form of a surface are disclosed. According to one embodiment, the apparatus comprises a linear light source including a light diffuser. The apparatus also has a sheet having a first edge with the linear light source placed along the first edge. The linear light source diffuses light emitted from a primary light source such that the light emanates along the first edge of the sheet. The linear light source is also substantially transparent to light exiting from the first edge of the sheet.

The present application is a continuation of patent application Ser. No.11/754,227 entitled “ENERGY EFFICIENT ILLUMINATION FOR A LIGHT SOURCE INTHE FORM OF A SURFACE” filed on May 25, 2007 at the USPTO, which in turnclaimed the benefit of and priority to Indian Provisional PatentApplication No. 800/MUM/2006 entitled “ENERGY EFFICIENT ILLUMINATION FORLIGHT SOURCE IN THE FORM OF A SURFACE” and filed on May 25, 2006.

FIELD

The present invention relates to an illumination system. Particularly,the invention relates to an apparatus for energy efficient illuminationfor a light source in the form of a surface.

BACKGROUND

Illumination is used to light objects for seeing, as also forphotography, microscopy, scientific purposes, entertainment productions(including theatre, television and movies), projection of images and asbacklights of displays. For illumination purposes, systems in the formof point or single dimensional sources of light are used. Such systemshave many drawbacks: light intensity is very high at the light sourcecompared to the rest of the room or environment, and thus such lightsources are hurtful to the eye. Such sources also cast very sharpshadows of objects, which are not pleasing to the eye, and may not bepreferred for applications such as photography and entertainmentproduction. Such sources also cause glare on surfaces such as tabletops, television front panels and monitor front panels.

There are systems that act as light sources in the form of a surface.Fluorescent lights for home lighting may be covered by diffuser panelsto reduce the glare. These systems are bulky. They are also nottransparent. Diffusers and diffuse reflectors, such as umbrellareflectors, are used as light sources for photography andcinematography, but they are only approximations to uniform lighting.

Backlights of flat-panel screens such as LCD screens provide uniform oralmost uniform light. One of the prior solutions for backlighting an LCDscreen is to have a light guide in the form of a sheet, with some shapessuch as dots or prisms printed on it to extract light or by dispersinglight diffusing particles in the bulk. The light guide is formed bysandwiching a high refractive index material between two low refractiveindex materials. The light is guided from one or more ends of the sheet.

These light sources in the form of a surface actually just redirect thelight from some other primary light source, in some predeterminedemanation pattern. This primary source of light has to be coupledefficiently to the light source in the form of a surface. Light sourcesused for this application include CCFL tubes, array of LEDs etc.

Two CCFL tubes, one at each end of the sheet may be used. Each CCFL tubeis placed inside a reflecting trough having a rectangular cross section.The light from the CCFL tube is coupled to the sheet. The disadvantageof this method is that the light may have to undergo many reflectionsbefore it enters the sheet. Each of these reflections cause some wastageof light and leads to inefficiency. Moreover, there is no control on thedirection in which the light enters the sheet. Some part of light isreflected back into the CCFL and this leads to further wastage of light.Some part of the light entering the edge of the backlight sheet exitsthe opposite edge. Part of this light falls upon the opposite CCFL, andis lost, leading to further inefficiency.

Flat screen color displays normally use illumination in the form ofwhite light. The white light falls on the display such as a LCD whichuses color filters to depict colors. Color filters reduce efficiency ofthe display since large amounts of light are absorbed. Anotherdisadvantage is that because of the color filters, the transmittance ofthe display is very low. To avoid using color filters, colored lightneeds to be used. This colored light has to be coupled properly todisplay the correct colors.

SUMMARY

An apparatus and method for coupling light into a light source in theform of a surface are disclosed. According to one embodiment, theapparatus comprises a linear light source including a light diffuser.The apparatus also has a sheet having a first edge with the linear lightsource placed along the first edge. The linear light source diffuseslight emitted from a primary light source such that the light emanatesalong the first edge of the sheet. The linear light source is alsosubstantially transparent to light exiting from the first edge of thesheet.

The above and other preferred features, including various details ofimplementation and combination of elements are more particularlydescribed with reference to the accompanying drawings and pointed out inthe claims. It will be understood that the particular methods andsystems described herein are shown by way of illustration only and notas limitations. As will be understood by those skilled in the art, theprinciples and features described herein may be employed in various andnumerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as part of the presentspecification, illustrate the presently preferred embodiment andtogether with the general description given above and the detaileddescription of the preferred embodiment given below serve to explain andteach the principles of the present invention.

FIG. 1A illustrates a block diagram of an exemplary light source systemas seen from the front, according to one embodiment.

FIG. 1B illustrates a block diagram of an exemplary light source systemas seen from a side, according to one embodiment.

FIG. 2A illustrates a block diagram of an exemplary light source systemas seen from the front, according to one embodiment.

FIG. 2B illustrates a block diagram of an exemplary light source systemas seen from a side, according to one embodiment of the invention.

FIG. 3 illustrates a block diagram of a light source system as viewedfrom the front, according to one embodiment.

FIG. 4 illustrates a block diagram of an exemplary element of a linearlight source column, according to an embodiment.

FIG. 5 illustrates a diagram of a linear light source having a variedconcentration of diffuser particles, according to one embodiment.

FIG. 6 illustrates an exemplary linear light source having two lightsources, according to one embodiment.

FIG. 7 illustrates a diagram of an exemplary mirrored linear lightsource, according to one embodiment.

FIG. 8 illustrates a block diagram of an exemplary light source of abacklight, according to one embodiment.

FIG. 9 illustrates a block diagram of an exemplary light source of abacklight, according to another embodiment.

FIG. 10 illustrates a block diagram of a light coupling system,according to one embodiment.

FIG. 11 illustrates a block diagram of a light coupling system,according to one embodiment.

FIG. 12 illustrates a block diagram of a light coupling system,according to one embodiment.

FIG. 13 illustrates a block diagram of a light coupling system,according to one embodiment.

FIG. 14 illustrates a block diagram of an exemplary light source of abacklight, according to one embodiment.

FIG. 15 illustrates a block diagram of an exemplary multicolored backlitdisplay, according to one embodiment.

FIG. 16A illustrates a block diagram of an exemplary column of anexemplary back-lit display system as viewed from the top, according toone embodiment.

FIG. 16B illustrates a block diagram of an exemplary column of a backlitdisplay system as viewed from the side, according to one embodiment.

FIG. 16C illustrates a block diagram of an exemplary column of a backlitdisplay system as viewed from the front, according to one embodiment.

FIG. 17A illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator, according to one embodiment.

FIG. 17B illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column as seen from the front,according to one embodiment.

FIG. 17C illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column as seen from the top,according to one embodiment.

FIG. 18A illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator, according to anotherembodiment.

FIG. 18B illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column, as seen from the front,according to another embodiment.

FIG. 18C illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column, as seen from the top,according to another embodiment.

FIG. 19 illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column, according to oneembodiment.

FIG. 20A illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column, according to oneembodiment.

FIG. 20B illustrates a block diagram of an exemplary light sourceilluminating a multicolored illuminator column, according to oneembodiment.

FIG. 21 illustrates a block diagram of an exemplary light sourceilluminating a linear light source according to one embodiment.

FIG. 22 illustrates a block diagram of an exemplary light sourceilluminating a linear light source according to one embodiment.

DETAILED DESCRIPTION

An apparatus and method for coupling light into a light source in theform of a surface are disclosed. According to one embodiment, the systemcomprises a linear light source placed along an edge of the light sourcein the form of a surface. The linear light source includes adistribution of dispersing material. The dispersing material disperseslight traveling in the linear source of light and couples it to thelight source in the form of a surface. The linear light source is alsosubstantially transparent to light exiting from the light source in theform of a surface.

According to an embodiment, an apparatus to efficiently couple thelinear source of light and the light source in the form of a surface isdescribed.

According to another embodiment, an apparatus to efficiently couple thecolored linear sources of light and the multicolored backlight sheet isdescribed.

According to another embodiment, an apparatus to efficiently couple theprimary source of light such as an LED and the linear source of light isdescribed.

FIG. 1A illustrates a block diagram of an exemplary light source system199 as seen from the front, according to one embodiment. A primary lightsource 100 is coupled to a linear light source 102. Primary light sourcecan be any point source of light including LEDs, LASERs, OLEDs, etc. Thelinear light source of 102 has a cylindrical waveguide of a transparentmaterial. A light source in the form of surface 104 (core), that is asheet of transparent material. In one embodiment, the refractive indexof the linear light source is greater than that of the core. The core104 also has a higher refractive index than cladding sheet 108. Linearlight source 102 has a sparse distribution of light diffusers. The lightdiffuser is one or more of a metallic powder, metallic pigment, organicpowder, and organic pigment. The light diffuser reflects incident light.In an alternate embodiment, the light diffuser is one or more of atransparent particle, and transparent bubble. The light diffuserdisperses light by refraction. The light traveling inside the linearsource of light gets scattered when it hits the dispersing particles andescapes from the linear source. Some of this light enters the core 104.The linear light source 102 is placed at a focus point of a reflectingsurface 106 which may be any light reflector, including metallicsurfaces, distributed Bragg reflectors, hybrid reflectors, totalinternal reflectors or omni-direction reflectors. In one embodiment, thereflecting surface is parabolic in shape. The light from the linearsource travels towards the reflecting surface 106 and is reflected intothe core 104. The core 104 is any light source in the form of a surface.The core 104 acts as a light source by dispersing light traveling in itby using dispersing particles in the bulk or by etching one or moresurfaces, etc. Mirror 109 is placed along each edge of core 104, exceptthe one along which the linear light source 102 is placed.

FIG. 1B illustrates a block diagram of an exemplary light source system199 as seen from a side, according to one embodiment. A primary lightsource 100 is coupled to a linear light source 102. A light source inthe form of surface 104 (core), that is a sheet of transparent material.The linear light source 102 is placed at a focus point of a reflectingsurface 106 that may be any light reflector. The light from the linearsource travels towards the reflecting surface 106 and is reflected intothe core 104. The core 104 also has a higher refractive index thancladding sheets 108. In alternate embodiments, the reflecting surface106 is elliptical, circular or rectangular in shape.

FIG. 2A illustrates a block diagram of an exemplary light source system299 as seen from the front, according to one embodiment. Primary lightsource 210 is coupled to the second linear light source 212 which isplaced along the edge of core 104 opposite to the one along which thefirst linear light source 102 is placed. The core 104 is any lightsource in the form of a surface. The core 104 acts as a light source bydispersing light traveling in it by using dispersing particles in thebulk or by etching one or more surfaces. Mirror 209 is placed along eachedge of core 104, except the edges along which the linear light sources102 and 212 are placed. The linear light source 102 is placed at a focuspoint of a reflecting surface 106 which may be any light reflector,including metallic surfaces, distributed Bragg reflectors, hybridreflectors, total internal reflectors or omni-direction reflectors. Thesecond linear light source 212 is placed at a focus point of areflecting surface 216 which may be any light reflector, includingmetallic surfaces, distributed Bragg reflectors, hybrid reflectors,total internal reflectors or omni-direction reflectors.

FIG. 2B illustrates a block diagram of an exemplary light source system299 as seen from a side, according to one embodiment. A light source inthe form of surface 104 (core) is a sheet of transparent material. Thelinear light source 102 is placed at a focus point of a reflectingsurface 106 that may be any light reflector. The light from the linearsource travels towards the reflecting surface 106 and is reflected intothe core 104. The core 104 also has a higher refractive index thancladding sheets 108. Primary light source 210 is coupled to the secondlinear light source 212 which is placed along the edge of core 104opposite to the one along which the first linear light source 102 isplaced. The second linear light source 212 is placed at a focus point ofa reflecting surface 216 which may be any light reflector, includingmetallic surfaces, distributed Bragg reflectors, hybrid reflectors,total internal reflectors or omni-direction reflectors.

FIG. 3 illustrates a block diagram of a light source system 399 asviewed from the front, according to one embodiment. Near one end of thelinear light source column 304, a light source 308 is placed. The lightsource 308 may be an LED, or other similar light source. The light fromthe light source 308 enters the linear light source column 304. In anembodiment, the light from the light source 308 enters the linear lightsource column 304 using an optical arrangement such as a focusingreflector. Linear light source column 304 comprises a diffuser which maybe constituted of small transparent particles or bubbles, which disperselight 314 by refraction, reflection at the boundary, by diffusion insidethe particle, by scattering, or by total internal reflection. The lightfrom the light source 308 is dispersed over the entire length of thelinear light source column 304, and exits in all directions. Lightexiting in the direction of the core, gets coupled to the core. Lightexiting in other directions may be recycled using reflectors such asthose described above in conjunction with FIG. 1A.

FIG. 4 illustrates a block diagram of an exemplary element 499 of alinear light source column 404, according to one embodiment. Element 499has a very small height. Light 400 enters element 499. Some of the lightgets dispersed and leaves the light guide as illumination light 402, andthe remaining light travels on to the next linear light source element.The power of the light 400 going into element 499 is matched by the sumof the powers of the dispersed light 402 and the light continuing to thenext element. The fraction of light dispersed 402 with respect to thelight 400 entering the element 499 is the photic dispersivity of element499. The photic dispersivity of element 499 is in direct proportion tothe height of element 499. The ratio of the photic dispersivity ofelement 499 to the height of element 499 is the photic dispersiondensity of element 499. As the height of element 499 decreases, thephotic dispersion density approaches a constant. This photic dispersiondensity of element 499 bears a certain relationship to the diffuserconcentration at the element 499. The relationship is approximated to acertain degree as a direct proportion. By knowing the diffuserconcentration of an element, the photic dispersion density of element499 may be evaluated, and vice versa.

As the height of element 499 is reduced, power in the emanating light402 reduces proportionately. The ratio of power of the emanating light402 to the height of element 499, which approaches a constant as theheight of the element is reduced, is the emanated power density atelement 499. The emanated power density at element 499 is the photicdispersion density times the power of the incoming light (i.e. power oflight traveling through the element). The gradient of the power of lighttraveling through the element 499 is the negative of the emanated powerdensity. These two relations give a differential equation. This equationcan be represented in the form “dP/dh=−qP=−K” where:

h is the distance of the linear light source element from the lightsource;

P is the power of the light being guided through that element;

q is the photic dispersion density of the element; and

K is the emanated power density at that element.

This equation is used to find the emanated power density given thephotic dispersion density at each element. This equation is also used tofind the photic dispersion density of each element, given the emanatedpower density. To design a particular linear light source with aparticular emanated power density, the above differential equation issolved to determine the photic dispersion density at each element of thelinear light source, such as linear light source 102. From this, thediffuser concentration at each element of a linear light source isdetermined. Such a linear light source is used in a light guide, to givea linear light source column of required emanated power density.

If a uniform concentration of diffuser is used in the linear lightsource, the emanated power density drops exponentially with height.Uniform emanated power density may be approximated by choosing adiffuser concentration such that the power drop from the edge near thelight source to the opposite edge, is minimized. To reduce the powerloss and also improve the uniformity of the emanated power, the oppositeedge reflects light back into the linear light source column 499. In analternate embodiment, another light source provides light into theopposite edge.

To achieve uniform illumination, the photic dispersion density and hencethe diffuser concentration has to be varied over the linear light sourcelength. This can be done using the above methodology. The requiredphotic dispersion density is q=K/(A−hK), where A is the power going intothe linear light source 304 and K is the emanated power density at eachelement, a constant number for uniform illumination. If the total heightof the linear light source is H, then H times K should be less than A,i.e. total power emanated should be less than total power going into thelight guide, in which case the above solution is feasible. If thecomplete power going into the light guide is utilized for illumination,then H times K equals A. In an embodiment, H times K is kept onlyslightly less than A, so that only a little power is wasted, as well asphotic dispersion density is always finite.

FIG. 5 illustrates a diagram of a linear light source column 599 havinga varied concentration of diffuser particles, according to oneembodiment. The concentration of the diffuser 502 is varied from sparseto dense from the light source edge (near light source 508) of linearlight source column 504 to the opposite edge.

FIG. 6 illustrates an exemplary linear light source column 699 havingtwo light sources 608, 609, according to one embodiment. By using twolight sources 608, 609, high variations in concentration of diffuser 602in the linear light source column 604 is not necessary. The differentialequation provided above is used independently for deriving the emanatedpower density due to each of the light sources 608, 609. The addition ofthese two power densities provides the total light power densityemanated at a particular core element.

Uniform illumination for light source 699 is achieved by photicdispersion density q=1/sqrt ((h−H/2)^(Λ)2+C/K^(Λ)2) where sqrt is thesquare root function, ^(Λ) stands for exponentiation, K is the averageemanated power density per light source (numerically equal to half thetotal emanated power density at each element) and C=A (A−HK).

FIG. 7 illustrates a diagram of an exemplary mirrored linear lightsource column 799, according to an embodiment. By using a mirroredlinear light source 704, high variations in concentration of diffuser702 in the core 704 is not necessary. Top end 710 of the central linearlight source column 704 is mirrored, such that it reflects light backinto linear light source column 704. The photic dispersion density toachieve uniform illumination in light source 799 is:

q=1/sqrt ((h−H)^(Λ)2+D/K ^(Λ)2)

where D=4A (A−HK).

For any illumination system (such as the light sources in the form ofsurfaces 599, 699 and 799), the same pattern of emanation is sustainedeven if the light source power changes. For example, if the light source708 of linear light source column 799 provides half the rated power,each element of the core 704 will emanate half its rated power.Specifically, a light guide core 704 designed to act as a uniform linearlight source acts as a uniform linear light source at all power ratingsby changing the power of its light source 708 or sources. If there aretwo light sources, their powers are changed in tandem to achieve thiseffect.

FIG. 8 illustrates a block diagram of an exemplary light source 899 fora backlight, according to one embodiment. Linear light source 802 isplaced at the focus of a parabolic reflecting surface 806. Light ray 810emanating out of the linear source 802 gets reflected from the reflector806 and enters into the core 804.

FIG. 9 illustrates a block diagram of an exemplary light source 999 fora backlight, according to one embodiment. Cladding sheet 914 of lowerrefractive index than transparent core 904 is used. The core 904 ismirrored at the edge which is opposite the edge with the linear lightsource 902. The mirror 908 maybe any reflector including those describedabove in conjunction with FIG. 1A. Light ray 910 emanating out of thelinear source 902 is reflected from the reflector 906 and enters intothe core 904. Light ray 912 which reaches mirrored edge 908 of the core904 gets reflected by the mirror 908. This ray 912 travels backwards andpasses through the substantially transparent linear source of light 902.It then gets reflected by the reflector 906 and again enters core 904.

FIG. 10 illustrates a block diagram of a light coupling system 1099,according to one embodiment. Linear light source 1002 is placed at afocus point of the parabolic reflecting surface 1010. Linear lightsource 1002 includes a sparse concentration of preferentially orientedparticles 1006. Particles 1006 are oriented such that they disperse mostof the light into the parabolic reflector 1010. Light ray 1012 emanatingout of the linear source 1002 is reflected from the reflector 1010. Thereflected ray of light 1014 reflects such that it is almost parallel tothe sides of core 1004. Light ray 1014 is thus efficiently coupled tothe core avoiding wastage of light in the core.

FIG. 11 illustrates a block diagram of a light coupling system 1199,according to one embodiment. Linear light source 1102 is placed at afocus point of the parabolic reflecting surface 1110. A portion of thetop surface of linear light source 1102 is covered by a reflectingsurface 1108. The reflecting surface 1108 maybe any reflector includingthose described above in conjunction with FIG. 1A. Light ray 1112 insidethe linear source 1102 gets reflected from the reflector 1108. Thereflected ray of light 1114 reflects from the parabolic reflector 1110such that it is almost parallel to the sides of core 1104. Light ray1114 is thus efficiently coupled to the core 1104 avoiding wastage oflight in the core 1104.

FIG. 12 illustrates a block diagram of a light coupling system 1299,according to one embodiment. Linear light source 1202 has a sparsedistribution of light diffuser particles 1206. A portion of the bottomsurface of linear light source 1202 is covered by reflecting surface1208. The reflecting surface 1208 maybe any reflector including thosedescribed above in conjunction with FIG. 1A. Light ray 1214 while insidethe linear source 1202 is reflected by the reflector 1208. The reflectedray of light is then incident on core 1204. Similarly upward travelinglight ray 1212 is incident on core 1204. The bottom surface 1220 of thecore 1204 is suitably shaped. In an embodiment, the bottom surface 1220is elliptical in shape. Rays 1212 and 1214 straighten inside core 1204and are efficiently coupled to the core 1204 avoiding wastage of light.

FIG. 13 illustrates a block diagram of a light coupling system 1399,according to one embodiment. Linear light source 1302 has a sparsedistribution of light diffuser particles in it. Linear light source 1302is placed within the cavity of the rectangular reflecting surface 1314.The reflecting surface 1314 may be any reflector including thosedescribed above in conjunction with FIG. 1A. Light ray 1303 inside thelinear light source 1302 is reflected by reflector 1314. The ray oflight 1303 may undergo one or more reflections and is then incident oncore 1304. Similarly upward traveling light ray 1305 is incidentdirectly onto the core 1304.

Controlling the Angle of Light Emanation

FIG. 14 illustrates a block diagram of an exemplary light source 1499 ofa backlight, according to one embodiment. Linear light sources 1402 and1403 are concentric transparent tubes placed at the focus of a parabolicreflecting surface 1410. In one of the embodiments, linear source 1402has a greater refractive index than linear light source 1403. In analternate embodiment, linear light sources 1402 and 1403 have the samerefractive index and are separated by a lower refractive index cladding.Origin point of ray of light 1412 emanating from linear source 1402 iscloser to the focus than the origin point of ray of light 1414 emanatingfrom linear source 1403. Rays 1412 and 1414 are reflected from theparabolic reflecting surface 1410 and result in reflected rays 1416 and1418 respectively. Ray 1416 entering the core 1404 will be more parallelthan ray 1418. The ray 1416 provides a tighter angle of emanation fromthe core surface as compared to ray 1418. The angle of emanation oflight from the core 1404 is controlled by controlling light fed tolinear sources 1402 and 1403.

Coupling of Light to the Multicolored Illuminator

FIG. 15 illustrates a block diagram of an exemplary multicolored backlitdisplay 1599, according to one embodiment. An image is displayed on aflat panel screen 1506. In an embodiment, the flat panel screen 1506 isan LCD screen. Sheet 1504 has a number of columnar illuminators. Eachilluminator illuminates one column of pixels. Different illuminatorsemanate light of different colors. Thus, light illuminating differentpixel columns is of different colors. In an alternate embodiment, theilluminator column is not vertical. The surface 1502 is a reflectingsurface which reflects light escaping the sheet 1504 in a directionopposite to the direction of screen 1506. Linear light sources 1508 area number of linear light sources, each carrying a particular color oflight. These linear light sources 1508 are placed inside the concavepart of the reflector 1510. FIG. 15 illustrates the complete displaysystem. Described henceforth, is a single column of the multicoloreddisplay system.

FIG. 16A illustrates a block diagram of an exemplary column 1699 of anexemplary backlit display system as viewed from the top, according toone embodiment. Polarizer 1608, liquid crystal 1610 and polarizer 1612together form light valve 1622 that modulates the intensity of lightpassing through it. Illuminator column 1604, cladding sheet 1606 andmirrors 1602, 1614 and 1616 together form a light guide 1620.Illuminator column 1604 has a higher refractive index than claddingsheet 1606. Light is guided inside the light guide 1620 by reflection ortotal internal reflection. Illuminator column 1604 has a sparsedistribution of light diffuser particles. The light diffuser may be oneor more of a metallic powder, metallic pigment, organic powder, andorganic pigment, wherein the light diffuser reflects incident light. Inan alternate embodiment, the light diffuser is one or more of atransparent particle, and transparent bubble. The light diffuserdisperses light by refraction. Back-mirror 1602 reflects light from theback surface of column 1604. Side-mirrors 1614 reflect light from theside surfaces of column 1604. Side-mirrors 1614 prevent light fromleaking into the adjacent columns. The mirrors 1602, 1614 and 1616 maybe any reflector including those described above in conjunction withFIG. 1A.

FIG. 16B illustrates a block diagram of an exemplary column 1699 of anexemplary backlit display system as viewed from the side, according toone embodiment. Light ray 1618 is guided inside the light guide 1620 byreflection or total internal reflection. Polarizer 1608, liquid crystal1610 and polarizer 1612 together form light valve 1622 that modulatesthe intensity of light passing through it. Illuminator column 1604,cladding sheet 1606 and mirror 1602 together form a light guide 1620.Illuminator column 1604 has a higher refractive index than claddingsheet 1606. Light is guided inside the light guide 1620 by reflection ortotal internal reflection. Illuminator column 1604 has a sparsedistribution of light diffuser particles. Back-mirror 1602 reflectslight from the back surface of column 1604.

FIG. 16C illustrates a block diagram of an exemplary column 1699 of abacklit display system as viewed from the front, according to oneembodiment. Side-mirrors 1614 reflect light from the side surfaces ofcolumn 1604. Side-mirrors 1614 prevent light from leaking into theadjacent columns.

FIG. 17A illustrates a block diagram of an exemplary light source 1799illuminating a multicolored illuminator 1740, according to oneembodiment. Light source 1799 has a number of linear light sources 1704.In one embodiment, the linear source of light is a transparent tube witha small concentration of microscopic dispersing particles as describedabove in conjunction with FIG. 1A. In an embodiment the dispersingparticles have special shapes for directional extraction of light.Linear light source 1704 is placed at the focus of a reflecting trough1706. In an embodiment, the shape of the trough 1706 is parabolic. Eachlight trough 1706 is partially covered by a mirror 1708. Mirrors 1708,1714 are situated such that they reflect light from the linear lightsources 1704 into corresponding columns of illuminator 1740. In one ofthe embodiments, one third of the area of the light trough 1706 iscovered with mirror 1708. The mirrors 1708, 1714 may be any reflectorincluding those described above in conjunction with FIG. 1A. Light of afirst color 1702 undergoes reflection due to mirror 1708 and mirror 1710and finally enters the corresponding illuminator column 1700.

FIG. 17B illustrates a block diagram of an exemplary light source 1799illuminating a multicolored illuminator column 1700 as seen from thefront, according to one embodiment. Linear light source 1704 is placedat the focus of a reflecting trough 1706. In an embodiment, the shape ofthe trough 1706 is parabolic. Each light trough 1706 is partiallycovered by a mirror 1708. The mirror 1708 may be any reflector includingthose described above in conjunction with FIG. 1A. Light of a firstcolor 1702 undergoes reflection due to mirror 1708 and mirror 1710 andfinally enters the corresponding illuminator column 1700.

FIG. 17C illustrates a block diagram of an exemplary light source 1799illuminating a multicolored illuminator column 1700 as seen from thetop, according to one embodiment. Light of a first color 1702 undergoesreflection due to mirror 1708 and mirror 1710 and finally enters thecorresponding illuminator column 1700. Each light trough 1706 ispartially covered by a mirror 1708.

FIG. 18A illustrates a block diagram of an exemplary light source 1899illuminating a multicolored illuminator 1840, according to anotherembodiment. Mirror 1810 reflects light back into the light trough 1706.Mirror 1810 may be any reflector including those described above inconjunction with FIG. 1A. It prevents wastage of light from regionswhere light extraction is not supposed to happen.

FIG. 18B illustrates a block diagram of an exemplary light source 1899illuminating a multicolored illuminator column, as seen from the front,according to another embodiment. Light of a first color 1702 undergoesreflection due to mirror 1708 and mirror 1710 and finally enters thecorresponding illuminator column 1700. Each light trough 1706 containinglight source 1704 is partially covered by a mirror 1810.

FIG. 18C illustrates a block diagram of an exemplary light source 1899illuminating a multicolored illuminator column, as seen from the top,according to another embodiment. Light of a first color 1702 undergoesreflection due to mirror 1708 and mirror 1710 and finally enters thecorresponding illuminator column 1700. Each light trough 1706 containinglight source 1704 is partially covered by a mirror 1810.

FIG. 19 illustrates a block diagram of an exemplary light source 1999illuminating a multicolored illuminator column, according to oneembodiment. Transparent tube 1900 includes spots 1902 of lightdispersing particles. When light source 1999 is illuminated with lightfrom an end, light is extracted at all such spots 1902. In anembodiment, such a light source 1999 is used in place of light source1704 of light source 1799, with the spots 1902 being aligned to themirrors 1708. To get the desired emanation of light such that samedensity of light is emanated at each spot, the differential equationpresented in conjunction with FIG. 3 needs to be suitably modified andsolved to get the disperser concentration at each spot.

FIG. 20A illustrates a block diagram of an exemplary light source 2099illuminating a multicolored illuminator column 2000, according to oneembodiment. The linear light sources 2004, 2006 and 2008 are all placedinside a single trough 2010. In an embodiment, the trough comprises aparabolic reflecting surface which may be any reflector including thosedescribed above in conjunction with FIG. 1A. The light extracted fromthe linear light source enters the multicolored illuminator column 2000.

FIG. 20B illustrates a block diagram of an exemplary light source 2099illuminating a multicolored illuminator column 2000, according to oneembodiment. The linear sources of light 2004, 2006 and 2008 aretransparent tubes with a small concentration of disperser particles2016. The light extracted from the linear light sources 2004, 2006 and2008 in trough 2002 enters the multicolored illuminator columns 2000,2020 and 2040. The disperser is added at spots adjacent to correspondingilluminator columns. Reflector 2050 causes a large portion of lightextracted from a particular linear source of light 2004 to enter thecorresponding illuminator column 2020.

Coupling of Primary Light Source to a Linear Light Source

In one embodiment, the linear light source is a transparent tube withmicroscopic diffuser particles in it. So light from some source iscoupled into this tube.

FIG. 21 illustrates a block diagram of an exemplary light source 2199illuminating a linear light source, according to one embodiment. Lightsource 2102 is a primary light source. In an embodiment, light source2102 is an LED. Some part of light source 2102 is inserted into thelinear light source 2104. Light ray 2100, enters linear light source2104. In an embodiment, light 2100 travels within the linear lightsource 2104 due to total internal reflection. In another embodiment,light 2100 travels within the linear light source 2104 due to reflectionfrom a reflecting surface. The reflecting surface may be any reflectorincluding those described above in conjunction with FIG. 1A.

FIG. 22 illustrates a block diagram of an exemplary light source 2299illuminating a linear light source, according to one embodiment. Lightsource 2202 is a primary light source. In an embodiment, light source2202 is an LED. Light ray 2206, emanating from light source 2202 ispassed through a lens 2200. In an embodiment, the lens 2200 istransparent and is made of glass or acrylic. Light ray 2206 may changeits direction after going through lens 2200. It enters linear lightsource 2204.

An apparatus and method for coupling light into a light source in theform of a surface are disclosed. It is understood that the embodimentsdescribed herein are for the purpose of elucidation and should not beconsidered limiting the subject matter of the present patent. Variousmodifications, uses, substitutions, recombinations, improvements,methods of production without departing from the scope or spirit of thepresent invention would be evident to a person skilled in the art.

1. An apparatus comprising: a linear light source including a lightdiffuser; a sheet having a first edge, the linear light source placedalong the first edge; and a primary light source near one end of thelinear light source; wherein the linear light source diffuses light fromthe primary light source such that light emanates along the first edgeof the sheet; and the linear light source is substantially transparentto light exiting the sheet through the first edge.
 2. The apparatus ofclaim 1, wherein the light diffuser comprises particles that areincluded in a sparse distribution such that the linear light sourceremains substantially transparent to light entering it from outside. 3.The apparatus of claim 1, wherein the light diffuser comprisestransparent particles.
 4. The apparatus of claim 1, wherein the lightdiffuser comprises particles that are included in a varyingconcentration such that the linear light source produces uniform light.5. The apparatus of claim 1, further comprising another primary lightsource near another end of the linear light source.
 6. The apparatus ofclaim 1, wherein the primary light source is a light emitting diode.